The present invention relates to a process for transferring a pigment image, prepared from an electrostatic charge image by treatment with a liquid developer, from a charge image carrier to a copy carrier, with the aid of an electric field.
The transport of liquid ink or toner to a charge pattern, by means of a transport surface in order to develop charge images is disclosed in U.S. Pat. No. 3,560,204. In the described process, the surface carrying the charge image is moved past an ink drum at a small distance, and a potential is applied to the conducting ink drum so that the colorant is attracted to the regions of the charge image. Although the application of liquid can be reduced by such a development process, and the image areas can be relatively well reproduced in the form of a statistical grid, it has been found, however, that the reproduction of half-tones is remarkably unsatisfactory. This also cannot be improved by varying the spacing between the charge image and the ink drum.
Another problem encountered with liquid development processes for electrostatic images is pollution of the environment arising from evaporation of substantial amounts of the dispersing fluid from the liquid developer.
There remains a need for an electrostatic copying process which comprises developing an electrostatic charge image and transferring the developed pigment image, which results in little environmental pollution and which also provides a good half-tone reproduction in view of the generally high state of copying technology.